You are right, the tags show the special characters. But that doesn’t cause any errors, it’s just the way the characters are shown in Discourse. If you go to https://your-site/tag/tebliğ it loads correctly. And if you need to use the URL somewhere else, where the special characters are not encoded correctly, you could use the corresponding UTF-8 encoding directly in the URL.
For example, you can generate the encoding for tebliğ in a site like this one. So, for tebliğ it would be
tebli%C4%9F and the url
https://your-site/tag/tebli%C4%9F will work as well as
https://your-site/tag/tebliğ in Discourse.